Tube mills, particularly ball mills, are quite well known. They consist essentially of a first grinding chamber, at least one second grinding chamber and a co-rotating partition disposed between the grinding chambers. They are used for the comminution of different materials in the most varied industrial sectors.
The material to be comminuted is comminuted in the grinding process by the freely moving mass of grinding media, and not only spherical elements but also elements in the shape of bars or bar sections are used as grinding media.
The use of separate grinding chambers makes possible the effective use of grinding media of differing geometric construction, particularly the use of different diameters in the case of spherical grinding media. The individual grinding chambers can also have different grinding media filling ratios.
The partitions in the tube mills serve the purpose of separating the grinding media charges in adjacent grinding chambers separate from one another and of transporting the mill feed material from one grinding chamber to the other. For this purpose it is usual to dispose in the partition a discharge arrangement through which the mill feed material which has entered the intermediate chamber via inlet openings is discharged via a discharge opening into the second grinding chamber.
In order to increase the efficiency of the tube mill, it is already known that mill feed material entering the partition from the first grinding chamber is divided into oversize material and fines, whereby the fines enter the second grinding chamber via a discharge opening and the oversize material is returned to the first grinding chamber via a discharge cone directly behind the partition.
In DE 378 026 a tube mill with a central discharge is proposed, in which not only the mill feed material from the first grinding chamber but also the mill feed material from the second grinding chamber passes into the partition and from there is jointly discharged and delivered to a classifying arrangement. The returned oversize material from the classifier is in turn divided into oversize material and fines and passed on to the first or second grinding chamber respectively.
In WO 00/12281 two separate grinding mills are proposed, each with a separate grinding chamber, each having a different internal diameter. The mill feed material of the first tube mill is delivered to a separate classifier, the oversize material being returned to the first tube mill and the fines being delivered to the second tube mill.
The object of the invention is to improve the efficiency of a tube mill as well as a method of comminution of lumpy mill feed material.